The exchange and maintenance of genetic information in Escherichia coli will be studied employing biochemical and genetic techniques. Enzymes known to be involved in genetic recombination such as exonuclease V will be amplified in vivo by construction of recombinant plasmids. Cooperative interactions between exonuclease I, exonuclease III, exonuclease V and DNA polymerase I will be studied in vitro employing homogeneous enzyme preparations. Employing specially constructed nuclease deficient strains, attempts will be made to identify and purify the gene products associated with recL, uvrD and uvrE. If possible these gene products will be cloned. The roles of exonuclease I, exonuclease III, and exonuclease V in the maintenance of ColE1 plasmids will be examined by use of genetic, biochemical and physical analysis of nuclease deficient strains harboring ColE1 and its drug resistant derivatives. Conditionally lethal mutants of E. coli which appear to map within the recC subunit of exonuclease V will be studied in greater detail. Exonuclease V activity obtained from these mutants will be examined for altered substrate specificity.